1. Field of the Invention
The present invention concerns means for controlling clearance in an inter-shaft bearing journal in a multi-spool gas turbine.
2. Description of the Prior Art
Multi-spool gas tubines have a bearing journal which supports one revolving shaft in relation to another, and which generally comprises a roller bearing inserted between an outer ring mounted upon the first shaft and an inner ring mounted upon the second. More precisely, the first, outer shaft may consist of the trunnion of the shaft line of the high pressure stage, while the second, inner shaft consists of the trunnion of the shaft line of the low pressure spool. In order to obtain satisfactory performance from bearing journals of this type, the most effective arrangements possible must be sought for lubricating and cooling the roller bearing.
French Pat. No. 2,001,380, filed Jan. 24, 1969, provides several solutions. This patent relates to a gas turbine engine in which one journal bearing supports a compressor shaft in relation to a stationary journal box, while another journal bearing supports the same shaft in relation to a short shaft carried by the fan shaft. Lubricant is fed from a common source to three groups of axial grooves located under the inner ring of the roller bearing and distributed to the various upstream and downstream zones through radial drill holes in said inner ring. The second journal bearing is supplied with lubricant that has passed through some of the grooves of the first journal bearing.
French Pat. No. 2,208,050, filed Nov. 23, 1973, provides another illustration of the solutions being used. As described in this patent, the inner surface of the tightening nut of the inner ring of a journal bearing's roller bearing comprises an annular recess that is supplied with oil. The oil is then distributed over the inner ring in order to lubricate and cool the roller elements. From here, it passes over the outer ring.
These earlier methods of setting up bearing journals are not, however, always entirely satisfactory, leaving certain problems unresolved. This appears particularly in applications to multi-spool gas turbines, which demand a higher level of performance and involve severe conditions of use. Thus, the environment of the bearing journal is submitted to centrifugal and thermal expansions and, in the application hereabove, where a bearing journal in a multi-spool gas turbine is mounted between a trunnion of the shaft line of the high pressure spool and a trunnion of the shaft line of the low pressure spool, considerable clearance has been observed in operation at maximum r.p.m.s, despite tight mounting and application of known techniques for lubricating and cooling the journal's roller bearing.
Other technical solutions applicable to bearing journals of the type being considered and known to men skilled in the art also allows vibration damping of shafts and roller through the use of a pressurized film of oil formed over a bearing ring. But these solutions also turn out to be inadequate in avoiding the appearance of the excessive operating clearance that is so damaging to the mechanical upkeep of these bearing journals.